The present invention relates to a centrifuge, particularly a separator, having an inlet tube and a distributor for introducing a material to be centrifuged into a centrifugal chamber bounded by a centrifugal drum. The centrifugal chamber includes a sieve essentially arranged coaxially with respect to the inlet tube and/or distributor. The distributor is designed such that it guides the material to be centrifuged into an area of the centrifugal chamber which is arranged radially outside the outer circumference of the sieve, such area being a solids collecting space. During centrifugal separating, a liquid component of the introduced material to be centrifuged flows radially from the outside toward the inside of the drum through the sieve. The present invention also relates to a method of operating and cleaning the centrifuge.
A centrifuge of the above-mentioned type and a method of its operation are known from German Patent Document DE 25 29 614 C2, which describes a device for the continuous rotation pressure filtration of liquid media. Filtrations in the sense of this document are sieve as well as membrane filtrations as well as micro- or ultra-filtrations. By a hydrostatic pressure difference, a concentrate flow component is generated parallel to the surface of the filter, for the purpose of which a hydrodynamic delivery pressure in the ring gap between the centrifugal drum and the coaxial drum-shaped filter element is generated in that the drum and the filter element are simultaneously acted upon by mutually different rotary frequencies. Allegedly, without the independent relative rotatability, an extremely surface-laminar cross-current component would be formed between the filters which has such a low efficiency that, already shortly after the start of the filtration, the fractionation process would cease as a result of polarization effects and pore sealing.
The separate rotatability of the sieve drum causes high constructive expenditures and thus considerably increases the costs of the centrifuge. For this reason, among others, it was found that the just-described solution has not been successful in practice.
It is also noted that, despite the relative rotatability of the sieve with respect to the centrifugal drum, a rerinsing of the membrane by a rinsing liquid is often required. However, such a rerinsing requires expenditures and interrupts the centrifuging operation for a considerable period of time.
The present invention further develops the initially described centrifuge such that, by simplified constructive and/or process-related expenditures, the problem of the clogging of the sieve by solid particles or the problem of an uncomplicated cleaning of the centrifuge is solved.
This is achieved, according to the present invention, by a centrifuge comprising an inlet tube a centrifugal drum and a centrifugal chamber bounded by the centrifugal drum. Also included is a sieve arranged in the centrifugal chamber coaxially with respect to one or both of the inlet tube and a distributor. A solids collecting space is in an area of the centrifugal chamber and is arranged radially outside an outer circumference of the sieve. The distributor arranged for introducing and guiding material to be centrifuged into the solids collecting space so that during centrifugal separation a liquid component of the introduced material flows radially from the solids collecting space toward an interior of the drum through the sieve. The solids collecting space is discontinuously closable so that when the solids collecting space is opened, a return flow of the liquid component takes place through the sieve from the interior of the drum.
The present invention also includes a method for cleaning the centrifuge.
As noted above, since the solids collecting space can be discontinuously closed, a return flow of the liquid component through the sieve takes place when the solids collecting space is opened up.
For discharging the solids, the solids collecting space is opened up particularly by opening a piston side valve, so that solids and/or contaminants attached to and/or deposited on the sieve or the sieve drum (and, under certain circumstances, also cloggings or cakings) are discharged through the opening(s) opened up by the piston slide valve.
In a simple fashion, this creates a cleaning effect of the sieve. This is because, when the piston slide valve is opened, liquid flows from the liquid discharge space through the sieve back into the solids collecting space, whereby solids clogging the sieve are now detached from the sieve and are discharged through the opening(s) opened up by the piston slide valve.
The present invention therefore utilizes the unexpected effect that, when the piston slide valves, which are known per se, are opened for discharging the solids, the sieve is cleaned in a simple manner which virtually does not interrupt the centrifuging operation. A special aspect of this cleaning is the fact that the return flow can take place without the additional use of a rinsing liquid and that, only after a relatively long operation, a rerinsing by means of such a rinsing liquid will be required. It should also be stressed that, because of modern control techniques, it is possible to control the emptying mechanism very precisely and thereby also control the cleaning effects in a desired manner.
As a result of the cleaning effect, a long service life of the membrane insert is therefore achieved without the requirement of a production stop because of clogging. As a result of the rapidity of the emptying mechanism and the realizable controlling of the discharge volume, the intensity of the cleaning effect can be controlled as a function of the product to be centrifuged.
The discharge of the concentrate by way of a separating plate or small tube, by way of ducts and nozzles outside the membrane insert is also conceivable. As a function of the product to be centrifuged, this may lead to a lengthening of the rerinsing intervals (emptying intervals). An automating of the point of time of the emptying, by monitoring the component discharged there, is also conceivable.
The draining of a partial flow of the concentrate by way of nozzles at the piston slide valve is also conceivable. For such a discharge by nozzles at the piston slide valve, reference is made to German Patent Document DE 22 14 487.
Instead of a piston slide valve, an analogously functioning, discontinuously operating opening mechanism can be used which is arranged radially outside the sieve drum.
The relative rotatability between the sieve drum and the drum shell therefore no longer has to be realized although, in principle, the lack of relative rotatability can also be combined with the present invention. In principle, the present invention can also be combined with the idea, also known per se, of a device for the continuous discharge of a solid component arranged in the solids collecting space, as long as the above-described flow-back effect is utilized for the cleaning.
It is possible to assign to and/or connect behind the sieve drum a stack of plates so that, after the clarification of the product in the sieve drum, a separation of different liquid components from one another can take place in the stack of plates.
In a particularly simple manner, the present invention combines the technology of modern piston slide valve separators, known per se, with the idea of a membrane sieve. This provides a type of “membrane separator” with the option of a component separation on the output side in a plate stack which, optionally in a surprising manner, easily solves the problem of the clogging of the sieves of the separators.
The solids collecting space preferably has a double-cone shape, and the sieve is designed as a membrane sieve, particularly as a ceramic membrane sieve.
Other aspects and novel features of the present invention will become apparent from the following detail description of the invention when considered in conjunction with the accompanying drawings.